My son is looking at buying the Genisi coupe. Whats the word on this car? How does it compare to the Mazda 3?
Depending on the age, experience and driving history (ie. accidents), either one of those cars could be quite pricey for your son to insure.
Both cars should prove to be reliable and enjoyable to drive. The Genesis will be sportier, meaning the ride will be a bit harsher, but it'll handle considerably better.
The Genesis is RWD which could get a young, 'enthusiastic' driver into difficulty in the winter months if he's not responsible with the power. Snow tires are an absolute must for the Genesis (though I'd endorse them for any car).
The Genesis interior is much smaller -- as is the trunk. If your son plans to carry passengers regularly or have a lot of gear to haul around (golf clubs, hockey gear, bicycle), the Genesis probably won't work.
I'd be happy to have either one -- they're both really great cars. It depends more on what your son's wants and needs are than anything.